1. Field of the Invention
The present invention relates to a keyboard assembly for use in electronic musical instruments such as an electronic piano.
2. Prior Art
According to a general construction of the conventional keyboard assembly employed in the electronic musical instrument, a plurality of keys, key switches, key stoppers, key guides and the like are supported by key frames which are fixed to a main body of the instrument. Each of the keys is supported by the key frame such that it can freely rotate about a predetermined fulcrum point. On the key frame, one key switch is provided in connection with the key. When each key is depressed down, the corresponding key switch is driven so that a key-on signal is produced.
FIG. 1 shows cross-sectional views illustrating a mechanical construction of the keyboard assembly. At a front edge portion of a key frame 8, there is provided a key guide 11 which functions to avoid a lateral swinging movement or a twisting movement of the key to be occurred when the key is depressed. The key frame 8 is made by use of a metal plate having a rectangular shape. The tip edge portion of the key frame 8 is bent, and then, a resin mold is formed to cover the bent portion of the key frame, so that the key guide 11 will be eventually formed. Or, the bent shape of the key frame is made by the resin, and then, a bent portion of the key frame which comes in contact with the key is covered by a flexible resin, so that the key guide 11 will be eventually formed as one part of the key frame. A key switch 10 is mounted on a circuit board 81 so as to form a switch-circuit assembly. This switch-circuit assembly is securely fixed to the key frame 8 by a screw 82. The key switch 10 contains a projecting member made of an elastic material such as rubber. When the key is depressed down, an actuator 6 which is attached to a lower surface of a key 1 presses down the projecting member of the key switch 10 so that the projecting member will be deformed. Thus, internal contacts (not shown) of the key switch 10 come in contact with each other so that the key switch 10 is turned on.
A guided member 4 is formed as a part of the key 1 such that the guided member 4 projects from an lower surface of the key 1. When the key 1 is depressed down, the guided member 4 is slid down by being guided by the key guide 11 of the key frame 8. A stopper element 5 is formed as a part of the guided member 4. When the key 1 is returned from a depressed position, the stopper element 5 comes in contact with the key guide 11 so that an upper-limit stopper will be emerged for the key 1. Incidentally, a numeral 3 designates a black key. The key 1 (i.e., white key) provides a projection 7 which projects downward from a common base-edge portion 2. This common base-edge portion is provided at back edge portions of the keys. This projection 7 is inserted into a hole 9 which is formed at a predetermined back-edge portion of the key frame 8, and then, the key 1 is fixed with the key frame 8 by a screw 83.
When assembling the key 1 and key frame 8 together, the projection 7 of the key 1 is temporarily mounted on the key frame 8; and then, the key 1 is slid on the key frame 8 in a horizontal direction so that the guided member 4 is engaged with the key guide 11; thereafter, the projection 7 is inserted into the hole 9. As described above, the key 1 should be slid on the key frame 8 in the horizontal direction because of the shape of the guided member 4. In other words, the stopper element 5 is horizontally extended from the guided member 4 in a backward direction (i.e., a left-side direction of FIG. 1), so that in order to engage the guided member 4, having a letter-L-like shape, with the key guide 11, the key should be horizontally moved in a backward direction just before the keyboard apparatus is assembled together.
When assembling the conventional keyboard apparatus, a certain lower-surface portion of the key 1 and the actuator 6 are moved in a horizontal direction with respect to the key switch 10 projected from the key frame 8 while being in contact with each other, and then, they are fixed together. Due to such fixing manner, the key switch 10 is sometimes deformed in a horizontal direction. If the key 1 and the key frame 8 are fixed together in such manner, the key switch 10 cannot operate well, which causes a problem in the function of the key switch 10 may not be completely carried out. In order to the aforementioned deformation which is caused by the force to be effected in a horizontal direction when fixing the key 1 and the key frame 8 together, the conventional technology provides some countermeasures by which the thickness of the rubber wall of the key switch 10 is enlarged or the hardness of the rubber is increased. Or, in order to do so, it is necessary to fix the key switch 10 to the key frame 8 by a harder strength. Another countermeasure is disclosed in U.S. Pat. No. 4,914,999 in which the key is vertically moved down to the key frame, and then, the key is inserted to be attached to the key frame. In order to do so, a special-designed valve-like structure is provided for the key frame, key switch and circuit board such that the stopper element 5 can be smoothly moved downward along the key guide 11 when fixing the key and the key frame together.
However, if the thickness of the rubber wall of the key switch 10 is enlarged or the rubber used for the key switch 10 is made harder as described above, a key-depression sensitivity should be deteriorated. In order to intensely fix the key switch with the key frame, a number of fixing members or a number of steps for fixing the key switch with the key frame should be increased. Further, the workers should pay a great attention to the fixing operation such that components of the key do not touch with the key switch when fixing the key and the key frame together. Such complicated fixing operation requires much working hours, or much manual skill is required for the workers.
In the aforementioned technique disclosed by the U.S. patent, the construction or the key unit and the key-frame unit should be complicated, and a complicated process is required when forming the key frame. In addition, the stopper element should be passed through a valve-like portion when fixing the key with the key frame. Such operation is required for each of the keys. Thus, the disclosed technique suffers from its complication.